ISS AES STUDY OF THE INITIAL GROWTH STAGE OF CU THIN-FILMS ON SI(111)-7X7

Initial growth stages of Cu thin films on Si(111)-7 x 7 surfaces have been studied by means of low energy ion scattering spectroscopy (ISS) and Auger electron spectroscopy (AES). Cu films have been deposited up to a coverage of 5 monolayers (ML's) at several substrate temperatures in a range from RT (room temperature) up to 600-degrees-C. Surface compositional variations during the film growth have been measured by our recently developed CMA-type ISS-AES analyzer; ISS determines the composition of the outermost layer, while AES does that of several layers of the specimen surface. The change of the Si and Cu AES peak intensities versus coverage suggests a so-called layer-by-layer like growth at RT and a layer-plus-island growth at high temperatures, in agreement with earlier papers. In contrast, ISS data show more complicated and interesting variations which cannot be fully explained by simplified growth models. The ISS result suggests the occrrence of compositional modifications caused, for instance, by atomic replacement of Cu and Si atoms in the intermixed first few layers.